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The telephone numbering plan for a telephone system includes an international dialing prefix, such as "00" or "011", which is added before the country calling code and is specific to the country from which the caller is dialling. Generally, as in the list below, the need for this prefix is indicated with a "+".

Zone 1 – North American Numbering Plan Area

Areas within NANPA (North American Numbering Plan Area) are assigned area codes as if they were all areas within one country. The codes below in format +1 XXX represent area code XXX within the +1 NANPA zone — not a separate country code.

Originally larger countries, such as the United Kingdom or France, were assigned two-digit codes (to compensate for their usually longer domestic numbers) and small countries, such as Iceland, were assigned three-digit codes; however, since the 1980s, all new assignments have been three-digit regardless of countries’ populations.

History

CCITT, the predecessor of the ITU Telecommunication Standardization Sector (ITU-T), developed the first formal list of telephone country codes. This list was included in the 1964 CCITT Blue Book, among other international telecommunication recommendations, which would eventually become ITU-T recommendation E.164.

An earlier system of country codes for European use was mentioned in the 1960 CCITT Red Book. Some of these country codes were retained in the CCITT country code assignments and remain in effect (e.g. France +33, United Kingdom +44).

^ abc Russia, Kazakhstan, and Abkhazia make up the Seventh World Numbering Zone. From August 2007, Kazakhstan changed all area codes to start with 7; however, 6 is also reserved for Kazakhstan. Digits 3, 4, and 5 are reserved for Russia. Abkhazia was assigned +7 840 for landline and +7 940 for mobile operators on 28 September 2009 (Abkhazia will also continue using +995 44). Other digits are reserved for Russia. Currently, there are no internationally accessible numbers starting with 0, 1, 2 or 5 – these are access codes and similar arrangements.

^ abcdefghijklmnopqrstuvwxyzaaabac This country or territory is part of the North American Numbering Plan (NANP), even though it may be geographically far from North America (Mexico is not included). The country code for all NANP countries is 1; the numbers that follow are used in the same way as area codes are in the U.S. and Canada.

^ On May 31, 2010, Sint Maarten will join the North American Numbering plan, at which time international dialing to that location will require +1 721.

^ Before it joins the NANP at the stated date, it will continue to use +599 along with the rest of the Netherlands Antilles.